C Null Pointer

What Is Null Pointer?

C program defines the states that for each pointer type, When a pointer variable is declared and initialized either by a Null value or by 0 explicitly then the pointer variable is said to be null pointer. Conceptually a null pointer is a pointer that points nowhere, it doesn't have an address of any function or a variable , instead pointer is initialized with zero or null to indicate that this pointer variable is still unused.

Syntax - Null Pointer

data type *variablename = NULL;

Void Pointer Dereferencing

Dereferencing pointer variable of void type is bit complex than usual pointer variable. Consider the following program which will not compile .

C Program - Null Pointer

#include <stdio.h>
int main()
{
int *iptr = NULL;
printf("\nValue of iptr = %u", iptr);
return 0;
}

Null Pointer vs Unintitialized Pointer

Being a programmer, in most cases we will uninitialize a pointer variable instead of initializing a Null value to it. Conceptually the null pointer is highly different from uninitialized pointer variable because null pointer points nothing whereas uninitialized pointer points to some garbage address.

C Program - Null Pointer vs Unintitialized Pointer

#include <stdio.h>
int main()
{
int *nptr = NULL, *ptr;
if(nptr == 0)
  printf(" *nptr is a Null pointer \n ");
else
  printf(" *nptr is a not a Null pointer \n ");
if(ptr == 0)
  printf(" *ptr is a Null pointer \n ");
else
  printf(" *ptr is a not a Null pointer \n ");
return 0;
}

Null Pointer Datatype

Null pointer doesn't belongs to any special datatypes. Datatypes such as char *, int *, float *, double *, long int*, void* are all can be a Null pointer.

What is Null?

Many programmers like you will not prefer to use a plain 0 to initialize the pointer variable to act as null pointer because 0 is of integer datatype and will scattered through their entire pograms, as 0 can represent either numbers or pointers. Therefore, to reduce the conflict, the C program introduces the null value, The NULL is the preprocessor macro which is defined in the #include<stdio.h> header files. Using null to initialize the null pointer is for stylistic convention only, the preprocessor will convert the null back into 0 at the time of compilation.

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